I love that idea. I was looking as the "documentation" for a web-framework yesterday. All I was getting was tutorials and videos, nothing that explained to me how the damn thing works. Most of my questions would have been answer more quickly with a simple "Here's how it works and here's the API".
A few times a week I browse the mailinglist archives for the OpenBSD cvs and misc lists. Why some people may see it as rude, I find it refreshing when the developers tell people that reading walkthrough, tutorials, quick start guides and googling isn't a substitute for learning how things work. Sadly few products/projects make it easy to learn how things work and focus solely on "here's how you do X/Y/Z. Just tell me how it works and I'll figure it out.
I honestly think that this "left-brain centric" approach is to blame for a lot of people picking wrong solution for the problems. Of cause people should know better and get a more in depth knowledge before picking a tools, but realistically that doesn't happen as often as we would like.
I think there would be a large audience for the type of documentation that your suggest and I believe that it would a lot of people, my self included, to be better developers.